1. Field of the Invention
The invention is directed to a position sensing device for use in an electronic sewing machine.
2. Background of the Invention
In electronic sewing machines of the type disclosed for example in U.S. Pat. No. 3,984,745 for "Sewing Machine Stitch Pattern Generation Using Servo Controls" and on which preselected stitch patterns may be formed automatically, information related to the positional coordination of the needle penetration for each stitch of each pattern is stored in the machine. The selected information is converted to positional analog signals which control closed-loop servo means including motor means that directly control the positions of stitch forming instrumentalities of the sewing machine to produce a pattern of stitches corresponding to the selected stitch information. Position sensors in the form of linear precision potentiometers have commonly been utilized to provide feed back signals to the motor means indicative of the positions of the stitch forming instrumentalities. However, such potentiometers have not proved to be entirely satisfactory because of the wiper arm in this type of device which must move along a resistance element to produce an output voltage and which after a rather short period of time wears to the point where the device ceases to function reliably.
It is a prime object of the present invention to provide an electronic sewing machine with a position sensor which isn't dependent upon the movement of a wiper arm across a resistance element, and which will function reliably over long periods of time providing a motor that drives stitch forming instrumentalities with feedback signals accurately representing their existing positions.